In television transmission systems, either black and white or color, the video and audio information, along with synchronizing signal components, are transmitted as part of a composite signal. It is desirable to include additional information beyond the picture and sound information presently transmitted for the purpose of channel identification and the like. A number of proposals have been made for adding auxiliary signals to the present composite television signals to convey such additional information.
In order to conserve the limited frequency spectrum space which is available for the transmission of signals in the portion of the spectrum allotted to television transmission, it is desirable to transmit such auxiliary information within the same frequency band already occupied by the present composite television signal alone. Auxiliary signal systems have been devised for permitting the transmission of information in addition to the conventional video and sound signals. Most of these prior art systems, however, result in noticeable degradation of the video information carried by the television signal, do not operate at a sufficiently high data rate to be very useful in conveying the additional information, or are unreliable.
Some prior art systems use an approach in which entire frames or fields of the television signal are replaced with frames or fields of an auxiliary image representative signal which may be detected and displayed in a separate receiver. Such systems, however, are subject to substantial data rate limitations. In addition, they cause serious degradation of the normal television signal, because the removal of the normal signal and its replacement with the auxiliary signal, interferes with the reproduction of the normal signals on the cathode ray tube of the receiver.
Another problem which exists in systems which add auxiliary signals to the standard television signals is that such systems often are subject to the production of false indicia in response to white noise or impulse noise interference in the transmission path between the transmitting station and the receiver.
Accordingly, it is desirable to provide a television receiver which responds to auxiliary signals transmitted from a transmitting station or locally from a remote control unit in the room in which the receiver is to be used, which signals can be employed to control various functions in the receiver, such as channel number display and the like. It also is desirable to provide an auxiliary signal system for use in conjunction with television receivers which aids in direct channel access and which also may be utilized as an aid to signal-seek tuning.